1. Field of the Invention
The present invention relates to a transistor structure. In particular, the present invention relates to the transistor structure with a wider bottom in the gate trench.
2. Description of the Prior Art
The transistor structure composed of the source, the gate and the drain is widely used in electronic products. The source/drain located respectively at the side of the gate are respectively electrically connected to the outside through the source/drain contact regions.
With the trend of the shrinkage of the critical dimension (CD), the space for forming the source/drain contact regions decrease dramatically. Taking the transistor structure of line width of 40 nm in the conventional process for example, the remaining width for forming the source/drain contact regions may be as little as 30 nm. When operational errors such as lithographic and alignment errors are taken into consideration, it is extremely difficult to form the source/drain contact regions of 30 nm width. Once the source/drain region has bad contact, its operational performance will be seriously jeopardized.
Therefore, it is needed to provide a novel transistor structure with sufficient source/drain contact regions in a smaller unit to maintain the operational performance.